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U.S. will send more troops to Iraq

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U.S. official tells CNN that potential threat from ISIS prompted troop escalation

Pentagon sending 300 more troops to Baghdad as protection forces

Mortar rounds strike gate of holy site in Samarra

The United States has increased its military presence in Iraq, ordering 300 more troops to the violence-ravaged nation, the Pentagon announced Monday.

ISIS militants have "continued to pose a legitimate threat to Baghdad and its environs," a U.S. official told CNN. "We have seen them reinforce themselves around Baghdad enough to convince us more troops was the prudent thing to do."

The new troops, 200 of whom arrived Sunday and Monday, will provide security for the U.S. Embassy, the Baghdad airport and other facilities in Iraq, Pentagon spokesman Rear Adm. John Kirby said.

The deployment includes "a detachment of helicopters and unmanned aerial vehicles, which will bolster airfield and travel route security," Kirby said in a written statement.

The airport is in western Baghdad about 12 miles (20 kilometers) by helicopter from the embassy in the capital's fortified Green Zone.

The 300 troops are in addition to 300 U.S. advisers who will help train Iraq's security forces. They will bring the total of American forces in Iraq to about 800 troops.

ReveredShiite shrine attacked

On Monday, Three mortar rounds hit the outer gate of a Shiite holy site in Samarra, killing one person and wounding 14, a spokesman for Iraqi Prime Minister Nuri al-Maliki said.

Al-Iraqiya, a state-run television network, reported that the Iraqi air force demolished the site where the mortars were fired.

The Al-Askariya mosque was heavily damaged by militants in February 2006. That attack triggered retaliatory attacks against Sunnis, and touched off the sectarian fighting that nearly tore the country apart.

The mosque houses the Imam Ali al-Hadi and Imam Hassan al-Askari shrine, one of the holiest sites for Shiite Muslims.

Samarra is about 80 miles (129 kilometers) north of Baghdad.

The death was one of 1,873 in June due to violence, according to the Interior Ministry, a figure that includes 355 Iraqi soldiers and 130 police officers.

That is a dramatic increase from the May death toll of 994 given by the United Nations and health officials in restive Anbar province. The U.N. said 144 of the people killed in May were civilian police officers.

ISIS declares caliphate

Emboldened by a weakened Iraqi government that is struggling to stop their murderous advance, extremists of the Islamic State in Iraq and Syria declared over the weekend that they have set up a caliphate spanning large areas of the two countries.

In a newly released audio message and written statement, purportedly from the official spokesman of ISIS, the group called on Muslims to swear allegiance to the caliphate, which means Islamic state.

The group said in the message Sunday, which CNN couldn't independently confirm, that its flag now flies from Aleppo province in northwestern Syria to Diyala province in eastern Iraq. It announced that it was changing its name to just the "Islamic State."

The ISIS statement was just one of the many developments in the fast-moving situation in Iraq over the weekend.

Iraq's government touted its military offensive to recapture Saddam Hussein's hometown of Tikrit from extremists, with some officials taking to state-run television over the weekend to declare that the army had defeated ISIS.

But residents in the city nestled along the Tigris River, about 140 kilometers (about 87 miles) northwest of Baghdad, gave a different account Sunday.

"There are no Iraqi troops here," one woman told CNN by telephone from Tikrit. The only presence, at least in her neighborhood, is the "Islamic state," she said, referring to ISIS.

Photos:The ISIS terror threat

Photos:The ISIS terror threat

Wounded passengers are treated following a suicide bombing at the Brussels Airport on March 22, 2016. The attacks on the airport and a subway killed 32 people and wounded more than 300. ISIS claims its "fighters" launched the attacks in the Belgian capital.

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Syrians gather at the site of a double car bomb attack in the Al-Zahraa neighborhood of the Homs, Syria, on February 21, 2016. Multiple attacks in Homs and southern Damascus kill at least 122 and injure scores, according to the state-run SANA news agency. ISIS claimed responsibility.

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Syrian pro-government forces gather at the site of a deadly triple bombing Sunday, January 31, in the Damascus suburb of Sayeda Zeynab. ISIS claimed responsibility for the attack, according to a statement circulating online from supporters of the terrorist group.

Wounded people are helped outside the Bataclan concert hall in Paris following a series of coordinated attacks in the city on Friday, November 13. The militant group ISIS claimed responsibility for the attacks, which killed at least 130 people and wounded hundreds more.

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Emergency personnel and civilians gather at the site of a twin suicide bombing in Beirut, Lebanon, on Thursday, November 12. The bombings killed at least 43 people and wounded more than 200 more. ISIS appeared to claim responsibility in a statement posted on social media.

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Smoke rises over the northern Iraqi town of Sinjar on November 12. Kurdish Iraqi fighters, backed by a U.S.-led air campaign, retook the strategic town, which ISIS militants overran last year. ISIS wants to create an Islamic state across Sunni areas of Iraq and Syria.

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Syrian government troops walk inside the Kweiras air base on Wednesday, November 11, after they broke a siege imposed by ISIS militants.

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Members of the Egyptian military approach the wreckage of a Russian passenger plane Sunday, November 1, in Hassana, Egypt. The plane crashed the day before, killing all 224 people on board. ISIS claimed responsibility for downing the plane, but the group's claim wasn't immediately verified.

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An explosion rocks Kobani, Syria, during a reported car bomb attack by ISIS militants on Tuesday, October 20.

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Shiite fighters, fighting alongside Iraqi government forces, fire a rocket at ISIS militants as they advance toward the center of Baiji, Iraq, on Monday, October 19.

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Smoke rises above a damaged building in Ramadi, Iraq, following a coalition airstrike against ISIS positions on Saturday, August 15.

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Iraqi men look at damage following a bomb explosion that targeted a vegetable market in Baghdad on Thursday, August 13. ISIS claimed responsibility for the attack.

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In this image taken from social media, an ISIS fighter holds the group's flag after the militant group overran the Syrian town of al-Qaryatayn on Thursday, August 6, the London-based Syrian Observatory for Human Rights reported. ISIS uses modern tools such as social media to promote reactionary politics and religious fundamentalism. Fighters are destroying holy sites and valuable antiquities even as their leaders propagate a return to the early days of Islam.

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An ISIS fighter poses with spoils purportedly taken after capturing the Syrian town of al-Qaryatayn.

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Smoke rises as Iraqi security forces bomb ISIS positions in the eastern suburbs of Ramadi, Iraq, on August 6.

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Buildings reduced to piles of debris can be seen in the eastern suburbs of Ramadi on August 6.

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The governor of the Asir region in Saudi Arabia, Prince Faisal bin Khaled bin Abdulaziz, left, visits a man who was wounded in a suicide bombing attack on a mosque in Abha, Saudi Arabia, on August 6. ISIS claimed responsibility for the explosion, which killed at least 13 people and injured nine others.

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Saudi officials and investigators check the inside of the mosque on August 6.

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Mourners in Gaziantep, Turkey, grieve over a coffin Tuesday, July 21, during a funeral ceremony for the victims of a suspected ISIS suicide bomb attack. That bombing killed at least 31 people in Suruc, a Turkish town that borders Syria. Turkish authorities blamed ISIS for the attack.

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Protesters in Istanbul carry anti-ISIS banners and flags to show support for victims of the Suruc suicide blast during a demonstration on Monday, July 20.

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People in Ashmoun, Egypt, carry the coffin for 1st Lt. Mohammed Ashraf, who was killed when the ISIS militant group attacked Egyptian military checkpoints on Wednesday, July 1. At least 17 soldiers were reportedly killed, and 30 were injured.

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Syrians wait near the Turkish border during clashes between ISIS and Kurdish armed groups in Kobani, Syria, on Thursday, June 25. The photo was taken in Sanliurfa, Turkey. ISIS militants disguised as Kurdish security forces infiltrated Kobani on Thursday and killed "many civilians," said a spokesman for the Kurds in Kobani.

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Residents examine a damaged mosque after an Iraqi Air Force bombing in the ISIS-seized city of Falluja, Iraq, on Sunday, May 31. At least six were killed and nine others wounded during the bombing.

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People search through debris after an explosion at a Shiite mosque in Qatif, Saudi Arabia, on Friday, May 22. ISIS claimed responsibility for the attack, according to tweets from ISIS supporters, which included a formal statement from ISIS detailing the operation.

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Iraqi soldiers fire their weapons toward ISIS group positions in the Garma district, west of the Iraqi capital of Baghdad, on Sunday, April 26. Pro-government forces said they had recently made advances on areas held by Islamist jihadists.

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A member of Afghanistan's security forces stands at the site where a suicide bomber on a motorbike blew himself up in front of the Kabul Bank in Jalalabad, Afghanistan, on Saturday, April 18. ISIS claimed responsibility for the attack. The explosion killed at least 33 people and injured more than 100 others, a public health spokesman said.

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Iraqi counterterrorism forces patrol in Ramadi on April 18.

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Thousands of Iraqis cross a bridge over the Euphrates River to Baghdad as they flee Ramadi on Friday, April 17.

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Yazidis embrace after being released by ISIS south of Kirkuk, Iraq, on Wednesday, April 8. ISIS released more than 200 Yazidis, a minority group whose members were killed, captured and displaced when the Islamist terror organization overtook their towns in northern Iraq last summer, officials said.

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Kurdish Peshmerga forces help Yazidis as they arrive at a medical center in Altun Kupri, Iraq, on April 8.

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A Yazidi woman mourns for the death of her husband and children by ISIS after being released south of Kirkuk on April 8. ISIS is known for killing dozens of people at a time and carrying out public executions, crucifixions and other acts.

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People in Tikrit inspect what used to be a palace of former President Saddam Hussein on April 3.

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On April 1, Shiite militiamen celebrate the retaking of Tikrit, which had been under ISIS control since June. The push into Tikrit came days after U.S.-led airstrikes targeted ISIS bases around the city.

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Iraqi security forces launch a rocket against ISIS positions in Tikrit on Monday, March 30.

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The parents of 19-year-old Mohammed Musallam react at the family's home in the East Jerusalem Jewish settlement of Neve Yaakov on Tuesday, March 10. ISIS released a video purportedly showing a young boy executing Musallam, an Israeli citizen of Palestinian descent who ISIS claimed infiltrated the group in Syria to spy for the Jewish state. Musallam's family told CNN that he had no ties with the Mossad, Israel's spy agency, and had, in fact, been recruited by ISIS.

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Iraqi Shiite fighters cover their ears as a rocket is launched during a clash with ISIS militants in the town of Al-Alam, Iraq, on Monday, March 9.

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Displaced Assyrian women who fled their homes due to ISIS attacks pray at a church on the outskirts of Damascus, Syria, on Sunday, March 1. ISIS militants abducted at least 220 Assyrians in Syria.

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Safi al-Kasasbeh, right, receives condolences from tribal leaders at his home village near Karak, Jordan, on Wednesday, February 4. Al-Kasasbeh's son, Jordanian pilot Moath al-Kasasbeh, was burned alive in a video that was recently released by ISIS militants. Jordan is one of a handful of Middle Eastern nations taking part in the U.S.-led military coalition against ISIS.

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A Kurdish marksman looks over a destroyed area of Kobani on Friday, January 30, after the city had been liberated from the ISIS militant group. The Syrian city, also known as Ayn al-Arab, had been under assault by ISIS since mid-September.

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Kurdish people celebrate in Suruc, Turkey, near the Turkish-Syrian border, after ISIS militants were expelled from Kobani on Tuesday, January 27.

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Collapsed buildings are seen in Kobani on January 27 after Kurdish forces took control of the town from ISIS.

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Junko Ishido, mother of Japanese journalist Kenji Goto, reacts during a news conference in Tokyo on Friday, January 23. ISIS would later kill Goto and another Japanese hostage, Haruna Yukawa.

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ISIS militants are seen through a rifle's scope during clashes with Peshmerga fighters in Mosul, Iraq, on Wednesday, January 21.

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An elderly Yazidi man arrives in Kirkuk after being released by ISIS on Saturday, January 17. The militant group released about 200 Yazidis who were held captive for five months in Iraq. Almost all of the freed prisoners were in poor health and bore signs of abuse and neglect, Kurdish officials said.

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Smoke billows behind an ISIS sign during an Iraqi military operation to regain control of the town of Sadiyah, about 95 kilometers (60 miles) north of Baghdad, on Tuesday, November 25.

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Fighters from the Free Syrian Army and the Kurdish People's Protection Units join forces to fight ISIS in Kobani on Wednesday, November 19.

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A picture taken from Turkey shows smoke rising after ISIS militants fired mortar shells toward an area controlled by Syrian Kurdish fighters near Kobani on Monday, November 3.

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Iraqi special forces search a house in Jurf al-Sakhar, Iraq, on Thursday, October 30, after retaking the area from ISIS.

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ISIS militants stand near the site of an airstrike near the Turkey-Syria border on Thursday, October 23. The United States and several Arab nations have been bombing ISIS targets in Syria to take out the militant group's ability to command, train and resupply its fighters.

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Kurdish fighters walk to positions as they combat ISIS forces in Kobani on Sunday, October 19.

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Heavy smoke rises in Kobani following an airstrike by the U.S.-led coalition on October 18.

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Cundi Minaz, a female Kurdish fighter, is buried in a cemetery in the southeastern Turkish town of Suruc on Tuesday, October 14. Minaz was reportedly killed during clashes with ISIS militants in nearby Kobani.

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Kiymet Ergun, a Syrian Kurd, celebrates in Mursitpinar, Turkey, after an airstrike by the U.S.-led coalition in Kobani on Monday, October 13.

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Alleged ISIS militants stand next to an ISIS flag atop a hill in Kobani on Monday, October 6.

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A Kurdish Peshmerga soldier who was wounded in a battle with ISIS is wheeled to the Zakho Emergency Hospital in Duhuk, Iraq, on Tuesday, September 30.

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Syrian Kurds wait near a border crossing in Suruc as they wait to return to their homes in Kobani on Sunday, September 28.

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A elderly man is carried after crossing the Syria-Turkey border near Suruc on Saturday, September 20.

Kurdish Peshmerga fighters fire at ISIS militant positions from their position on the top of Mount Zardak, east of Mosul, Iraq, on Tuesday, September 9.

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Displaced Iraqis receive clothes from a charity at a refugee camp near Feeshkhabour, Iraq, on Tuesday, August 19.

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Aziza Hamid, a 15-year-old Iraqi girl, cries for her father while she and some other Yazidi people are flown to safety Monday, August 11, after a dramatic rescue operation at Iraq's Mount Sinjar. A CNN crew was on the flight, which took diapers, milk, water and food to the site where as many as 70,000 people were trapped by ISIS. But only a few of them were able to fly back on the helicopter with the Iraqi Air Force and Kurdish Peshmerga fighters.

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Thousands of Yazidis are escorted to safety by Kurdish Peshmerga forces and a People's Protection Unit in Mosul on Saturday, August 9.

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Thousands of Yazidi and Christian people flee Mosul on Wednesday, August 6, after the latest wave of ISIS advances.

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A Baiji oil refinery burns after an alleged ISIS attack in northern Selahaddin, Iraq, on Thursday, July 31.

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A Syrian rebel fighter lies on a stretcher at a makeshift hospital in Douma, Syria, on Wednesday, July 9. He was reportedly injured while fighting ISIS militants.

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Children stand next to a burnt vehicle during clashes between Iraqi security forces and ISIS militants in Mosul on Tuesday, June 10.

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Iraq executions,atrocities on both sides

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The woman, who asked not to be identified over concerns for her safety, said she could hear the sounds of a fierce battle, in the form of shelling, being carried out by both sides.

Heavy shelling

A video posted on YouTube appears to support her assertion. A man gives a tour of the city to show, he says, that there were no Iraqi security forces on the streets on Saturday, the day Iraqi forces said they launched the offensive.

In the video, the man can be heard repeatedly saying "June 28, 2014," presumably to offer evidence of the date. He says "Thank God, Tikrit is safe and still in the hand of tribesmen and not troops of 'al-Haliki,' " a derogatory reference to al-Maliki that refers to his death.

Witnesses inside and outside Tikrit said Iraqi forces were heavily shelling the city. Two days ago, the air force dropped leaflets from helicopters, demanding that residents leave the city "for their safety."

A large number of people have fled Tikrit for smaller villages to the north, according to witnesses, who say Iraqi forces are battling ISIS on the southern edge of the city.

State-run Iraqi TV showed video footage of large plumes of black smoke billowing from the city. Another video, released by the Ministry of Defense, showed Iraqi troops and convoys loaded with heavy weapons driving through the desert. The video was titled "cleansing the road between Samarra and Tikrit."

CNN couldn't independently confirm the different claims.

Russian jets arrive

Five Russian Sukhoi fighter jets have arrived in Iraq, the first of 25 warplanes expected to be delivered under a contract between Moscow and Baghdad, the Iraqi Ministry of Defense said in a statement.

A video the ministry released Monday showed the jets, with wings unattached, being pulled toward hangars.

"These jet fighters will contribute to increase the combat capability of the air force and the rest of the armed forces in eliminating terrorism," the ministry said.

The Su-25 has been in service for more than three decades and was part of the Iraqi air force under Saddam Hussein's regime.

The announcement follows a comment by al-Maliki that recent militant advances might have been avoided if Iraq had proper air power in the form of fighter jets that Iraq has been trying to get from the United States.

"I'll be frank and say that we were deluded when we signed the contract" with the United States, al-Maliki told the BBC in the interview last week, which was released Friday.

Iraq has now turned to Russia and Belarus to buy fighter jets, he said. "God willing, within one week, this force will be effective and will destroy the terrorists' dens," he said.

U.S. officials were quick to reject al-Maliki's complaints.

U.S. fighter jets have not been slow in coming, Kirby said. The first two promised F-16s "weren't expected to be delivered until the fall, which is still months away," Kirby said. "And we were in the process of working towards that delivery."

The advance of the al Qaeda splinter group "couldn't have been stemmed through the use of two particular fighter planes," he said.

Al-Maliki's statements about the need for air support came as American and Arab diplomats told CNN that the United States is unlikely to undertake any military strikes against the Islamic State of Iraq and Syria and its allied fighters before a new government is formed in Iraq.

Mass graves reported

Human Rights Watch has reported the discovery in Tikrit of two mass graves believed to contain the bodies of Iraqi soldiers, police and civilians killed by ISIS and its militant allies.

In addition to the alleged executions in Tikrit, reports continue to emerge of atrocities committed by both sides.

Human Rights Watch, citing displaced residents and local activists and journalists, said Saturday that ISIS fighters kidnapped at least 40 Shiite Turkmens, dynamited four Shiite places of worship and ransacked homes and farms in two villages just outside Mosul.

The few Sunni villagers who remained in Guba and Shireekhan told those who fled that at least some of the kidnapped Turkmens had been killed, the rights group said. However, they had not seen bodies and could not give more information.

ISIS destroyed seven Shiite places of worship in the predominantly Shiite Turkmen city of Tal Afar, about 50 kilometers (31 miles) west of Mosul, earlier in the week, Human Rights Watch added, citing local sources.

But the allegations of atrocities are not just limited to ISIS. Amnesty International has said it has gathered evidence pointing to a pattern of "extrajudicial executions" of Sunni detainees by government forces and Shiite militias in Tal Afar, Mosul and Baquba.